The present invention relates to a golf club head, and more particularly to an improved face plate forming a part of or forming the entire impact front face of a club head on which a gold ball is hit.
It is generally known that a golf club head is comprised of a single type of material or a combination of many different types of materials such as wood, metal, carbon and synthetic resins.
It is also generally recognized that the greater the degree of hardness of the face plate, the greater the restitution coefficient will be between the golf ball and the golf club upon impact with the face plate, and that the greater the restitution coefficient will be between the golf ball and the golf club, and also the greater will be the distance travelled by the golf ball. This is taught for example, by U.S. Pat. No. 4,181,306 to Jepson (Column 1, lines 36 to 39). In fact, many wood-type golf club heads, each having a face plate made of a hard material such as stainless steel, ABS resin or the like, have been proposed and are now available in the commercial markets. On the other hand, many iron-type gold club heads currently available are entirely made of metal such as stainless steel which is naturally hard, and for that matter, provides a hard metallic impact front face. Thus, it has been the general and conventional concept that it is unnecessary to provide the iron-type golf club head with a face plate.
In general, every golfer has a strong desire to increase the distance travelled by a golf ball which the golfer has hit (hereinafter referred to as "flying distance"). Therefore, a golfer is always looking for an improved golf club which enables such a desired increase in the flying distance traveled by a golf ball. However, it appears to be very difficult to meet the golfer's demand, as long as the conventional concept that, the greater the degree of hardness of the face plate, the greater the flying distance which can be obtained, is adhered to.
Among the various known materials for conventional face plates, both balata and gutta-percha have a compression Young's modulus in the range 0.6 Kg/mm.sup.2 to 2 Kg/mm.sup.2, which value is too small to enable a golf ball to travel a long flying distance. Thus the material for a face plate taught by U.S. Pat. No. 723,258 for Felton and U.S. Pat. No. 3,359,231 for Kent (balata and gutta percha resin) are some of the worst materials that can be use for a face plate, since these materials are too soft ABS resin is considered to be small in compression Young's modulus E, the value of which is as small as about 280 kg/mm.sup.2. It has been considered that materials having compression Young's modulus E values which are substantially smaller than 280 Kg/mm.sup.2 cannot be practically useful in the manufacture of face plates, although it has been known to use an ionomer resin having a Young's modulus E of about 20 kg/mm.sup.2 to 50 Kg/mm.sup.2 for a golf ball (Modern Plastics Encyclopedia, 1976-1977, Pages 32 to 33). Nevertheless, according to the present invention, a specific synthetic resin, having a compression Young's modulus E value which is extremely small, is utilized as the material for a face plate. Thus, it can be said that the present invention is based on a far departure from the conventional sense and knowledge in the field of golf clubs.
It is, therefore, an object of the present invention to provide an improved golf club head which permits an increase in the flying distance of a golf ball hit thereby.
Another object of the present invention is to provide an improved golf club head having a face plate which is formed of an ionomer resin having a compression Young's modulus value which is in the range of 20 to 50 Kg/mm.sup.2.